1. Field of the Invention
The present invention relates to an airfoil of each of blades constituting a compressor blade row, and particularly to a high turning airfoil in a compressor in which both of an intrados generating a positive pressure and an extrados generating a negative pressure exist on one side of a chord line.
2. Description of the Related Art
An airfoil for an airplane described in U.S. Pat. No. 4,655,412 has a feature in a distribution of curvature of an extrados thereof. The curvature has a first minimum value at a position in front of a position corresponding to 10% of a chord length; a second minimum value at a position in the rear of the position of the maximum value and in front of a position corresponding to 40% of the chord length, and a maximum value at a position intermediate between the first and second minimum values, whereby an enhancement in dynamic lift characteristic and an enhancement in load balance at a large elevation angle are provided by such distribution of curvature.
In an airfoil for a stator blade or a rotor blade of an axial flow compressor described in Japanese Patent No. 2,906,939, the curvature of an extrados has a minimum value at a position in the rear of a leading edge and a maximum value at a position in the further rear of the leading edge. Therefore, the generation of a shock wave is avoided in an inlet speed region from a high subsonic speed to a supersonic speed of the axial flow compressor, whereby a decrease in loss due to the shock wave is achieved.
The airfoil described in U.S. Pat. No. 4,655,412 is one for an airplane having a small turning angle and is difficult to be applied to a blade of a high turning axial flow compressor. The airfoil described Japanese Patent No. 2,906,939 is used for an axial flow compressor, but is of a low-turning type having an intrados and extrados existing on opposite sides of a blade chord line, and is basically different from an airfoil according to the present invention in which an intrados and extrados exist on one side of a blade chord line. In addition, in the airfoil described Japanese Patent No. 2,906,939, the curvature of the extrados has the maximum value in the rear of the minimum value, that is, the positional relationship between the maximum and minimum values is opposite from that in the airfoil according to the present invention in which the curvature of the extrados has the maximum value within a region from 10% to 35% of the chord length and the minimum value within a region from 30% to 50% of the chord length in the rear of the maximum value.
The present invention has been accomplished with the above circumstance in view, and it is an object of the present invention to provide a high turning compressor airfoil, wherein a laminar flow separation and the generation of bubbles particularly in a low Reynolds number region can be suppressed to reduce the relative total pressure loss, while maintaining a performance in medium and high Reynolds number regions.
To achieve the above object, according to a first feature of the present invention, there is proposed an advanced high turning compressor airfoil, in which both of an intrados generating a positive pressure and an extrados generating a negative pressure exist on one side of a blade chord line, wherein the curvature of the extrados made non-dimensional by a chord length has a maximum value between a position corresponding to 10% of the chord length and a position corresponding to 35% of the chord length, and a minimum value in the rear of the maximum value and between a position corresponding to 30% of the chord length and a position corresponding to 50% of the chord length.
According to a second feature of the present invention, in addition to the first feature, a difference between the maximum value and the minimum value of the curvature of the extrados is equal to or larger than 0.5.
According to a third feature of the present invention, in addition to the first feature, a turning angle is equal to or larger than 40xc2x0.
With above features, the curvature of the extrados of the high turning airfoil for the compressor in which the intrados generating the positive pressure and the extrados generating the negative pressure exist on one side of the chord line, has the maximum value between the position corresponding to 10% of the chord length and the position corresponding to 35% of the chord length, and the minimum value in the rear of the position of the maximum value and between the position corresponding to 30% of the chord length and the position corresponding to 50% of the chord length. Therefore, it is possible to suppress a laminar flow separation and the generation of bubbles in a low Reynolds number region to decrease the relative total pressure loss remarkably, without deteriorating the performance in medium and high Reynolds number regions.
Especially, the above effect can be exhibited further remarkably by setting the difference between the maximum and minimum values of the curvature of the extrados of the airfoil at 0.5 or more, or by setting the turning angle at 40xc2x0 or more.
The term xe2x80x9ccurvaturexe2x80x9d used in this specification indicates one made non-dimensional by the chord length C. Namely, the curvature is an inverse number of a radius of curvature, but the radius of curvature is made non-dimensional by the chord length C. Therefore, if an actual radius of curvature is equal to the chord length C, the non-dimensional radius of curvature is 1.0, and the curvature is 1.0. If the actual radius of curvature is two times the chord length C, the non-dimensional radius of curvature is 2.0, and the curvature is 0.5. If the actual radius of curvature is one half of the chord length C, the non-dimensional radius of curvature is 0.5, and the curvature is 2.0.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.